Nuclear Magnetic Resonance has been applied to cellular systems. Fluorine attached to dopamine acts as an NMR probe of nerve microsacs. Rabbit, cow, pig and human platelets incubated with 4,6-difluoroserotonin gave insight into the similarities and differences of the amine storage vesicles in each species. Feasibility studies have begun on lithium-7 spin-lattice relaxation times as a probe in cellular system.